The invention relates to conductive structures in polymers, which can be employed in electrical engineering, electronics and microelectronics.
The use of polymers in electrical engineering, electronics and microelectronics for insulation purposes is well known. In this connection, the objective generally is to use, on the one hand, the well-known advantageous properties of polymers relative to metals, such as the freely selectable shaping, the flexibility, the slight weight, the easy means of processing and the practically unlimited chemical modifiability and, on the other hand, while retaining these positive properties, to use the polymers at the same time as electrically conductive materials. Different methods are employed to produce conductive polymeric materials (for example, B. R. Seymour, Conductive Polymers, Plenum Press, New York 1981 and H. Kuzmany, Electronic properties of polymers and related compounds, Springer Verlag, Berlin, Heidelberg, New York, 1985).
The known solutions for producing conductive layers, for example, by introducing low molecular weight charge-transfer (CT) complexes in the polymer matrices (European Patents 0147 871 A2 and 0134 026 A1, U.S. Pat. No. 4,478,922), the treatment with suitable oxidizing and reducing agents (see R. Seymour, Conductive Polymers) or the admixture of carbon black (T. Slupkowski, Phys. stat. sol. (a) 90 (1985) 737-741) are not suitable for selective structuring in the .mu.m range, as required, for example, for printed conductors in microelectronics or the products do not exhibit the resistance to environmental effects which is required for application.
The previously known methods for achieving electrically conductive structures in polymers are very costly to realize technically and the end products exhibit an unfavorable environmental behavior.
For example, a method is described in German Offenlegungsschrift 2,627,828, in which a solution containing an organic .pi.-electron donor compound and a halogenated hydrocarbon is applied to a substrate, after which the substrate is illuminated with actinic radiation in a predetermined pattern. The excess solvent and/or the halogenated hydrocarbon are/is then evaporated off. The compounds, used in the German Offenlegungsschrift 2,627,828, are of the donor X.sub.n type. The donor originates predominantly from the group comprising tetrathiafulvalene, tetraselenafulvalene, and cis/trans diselenadithiafulvalene and X originates from the group comprising F, Br, Cl, and I (n&lt;1).
In addition, dyes are used when a layer combination is employed in the technically relevant visible spectral excitation region. The disadvantage of this multicomponent system consists predominantly of the complicated layer structure and thus of the expensive manner of producing the layers. Moreover, many CT complexes exhibit a decrease in electrical conductivity with duration of storage, so that the layers must be stabilized as well (for example, by protective coatings). These protective coatings generally are technically very expensive to realize, for example, by corona discharge polymerization, or require special polymers (for example, J. E. Osterholm et al., J. of Appl. Polymer Sci. 27 (1982) 931-936). If the layers are used for a printed circuit board, these necessary measures are very disadvantageous (for example, bonding).
Known solutions for producing printed conductors, setting contacts and contacts, in which metals are substituted for partially or completely, are based on the used of compositions with metallic, conductive components, such as silver particles (U.S. Pat. No. 4,289,534), gold particles (U.S. Pat. No. 4,230,493) or on the use of additives such as conductive carbon black, graphite, iron oxide, copper or aluminum particles, etc. (for example, M. J. Mair, Gummi, Faser, Kunststoffe 38 (1985) 3, 122-124). For example, in DD Patent 221,868 A1, a method is disclosed, in which compositions are used to produce printed conductors, the conductive components of which comprise carbon black or graphite particles. The lacquer with even more additives is sprayed, for example, on a conductive template, printed conductors resulting with a specific resistance of 2.times.10.sup.4 .OMEGA. mm.sup.2 /m (60% by weight of graphite). It is, however, a disadvantage of this method that a selective and also computer-supported microstructuring, which permits different printed circuit board elements (printed conductors, active and passive system components) to be produced in the shortest time and in the smallest space, is not possible.
Other methods consist of producing electrically conductive materials through pyrolysis (pyroconversion) of polymers (for example, J. Simitzis, Makromol. Chem. 185 (1984) 2569-2581). Thermal degradation of polymers leads to materials which contain carbon in different modifications and are very resistant to the effects of high temperature and chemicals. It is an important disadvantage of the previously synthesized polymers that, on the one hand, they are not good film formers and, on the other, that the pyrolysis temperatures to produce the required conductivities are very high, for example 700.degree. C. in the case of polyphenylenes. Pyrolysis products, produced at these temperatures, generally no longer have any coherence (J. Simitzis, Makromol. Chem 185 (1984) 2569-2581). It is a further disadvantage that the pyrolysis predominantly must taken place under inert conditions, as a result of which the technical effort involved is increased appreciably.